1. Technical Field
The present invention relates, in general, to an improved bioinstrumentation signal-processing system and, in particular, to an improved bioinstrumentation signal-processing system having the ability to distinguish man-made electrical signals within the body from physiological electrochemical activity. Still more particularly, the present invention relates to an improved bioinstrumentation signal processing system having the ability to distinguish man-made electrical activity within the body from physiological electrochemical activity by calculating the conduction velocities of detected electrical signals.
2. Description of the Related Art
The heart pumps blood by organized successive contraction of individual heart muscle fibers. A neurological signal spreads through the heart, and each muscle fiber responds by contracting in sequence. The overall effect is a single heartbeat, or heart pulse, moving blood through the heart. For effective pumping, the muscle fibers must contract in an organized fashion.
The neurological signal alluded to in the previous paragraph is effectuated by the spread of an action potential throughout the heart. An action potential is a transient change in cell membrane potential which conveys information, such as the information in a signal telling a heart muscle fiber to contract. When the heart muscle is at rest, the electrical potential on either side of any cell membrane is maintained at a fixed potential. However, when the muscle is stimulated, either electrically, chemically, or mechanically, channels open in the membrane which allow the oppositely charged ions on either side of the membrane to cross the membrane, such ions engaging in an effort to reach electrical and thermal neutrality. This occurrence is referred to as "depolarization" since the system is becoming less polarized as the ions tend toward the lowest energy state. If the stimulation is great enough, the change in potential arising from the ions crossing the membrane will be great enough to depolarize the portion of the membrane directly adjacent to the area of the membrane depolarized by the stimulus. When this occurs, an action potential is said to have been initiated, and the signal will continue to propagate through the fiber via the just described mechanism of depolarizing that portion of the membrane directly adjacent to the depolarized area. This propagation of the action potential is analogous to the way in which a row of dominoes falls when the first is flicked into the second, and the second falls into the third, and the third falls into the fourth, etc. Once the action potential has propagated past a region of the membrane, the cell membrane resets itself in a process known as "repolarization." In repolarization, ions are actively pumped back across the cell membrane to restore the polarized state.
In addition to the ions involved in the propagation of the action potential, there are numerous other free-floating ions distributed throughout the body. These ions will move under the influence of sufficiently strong electric fields. When the action potentials within the heart propagate, the ions moving across the cell membrane will disturb the electric fields within the body. This physiological electrochemical activity can be conducted to the body's surface via the reaction of the free-floating ions, which move in response to the electric-field effect of the charges crossing the membrane.
In the late 1800s, the Dutch physiologist Dr. Willem Einthoven developed techniques for recording this electrical activity of the heart, for which he was awarded a Nobel prize. The basic technique of Dr. Einthoven is still in use today. Dr. Einthoven's technique is known as the electrocardiogram, which is still referred to in honor of Dr. Einthoven as the EKG, which arises from the Dutch spelling of electrocardiogram.
During an EKG, electrodes are attached to the body surface. The electrodes are specially treated to allow the charge carrier within the electrodes (electrons) to communicate with the charge carriers within the body (ions) via electrochemical exchange. Attaching electrodes to the body surface allows the voltage changes within the body to be recorded after adequate amplification of the signal. A galvanometer within the EKG machine is used as a recording device. Galvanometers record potential differences between two electrodes. The EKG is merely the recording of differences in voltage between two electrodes on the body surface as a function of time, and is usually recorded on a strip chart. When the heart is at rest, diastole, the cardiac cells are polarized and no charge movement is taking place. Consequently, the galvanometers of the EKG do not record any deflection. However, when the heart begins to propagate an action potential, the galvanometer will deflect since an electrode underneath which depolarization has occurred will record a potential difference from a region on the body under which the heart has not yet depolarized.
A complete heart cycle is known as a heartbeat. On an EKG, the heartbeat has a distinctive signal. Initially, the galvanometer notes a small but sharp negative deflection (known as the Q wave). Next, there is a very large and sharp positive deflection (known as the R wave), after which there is a sharp and large negative deflection (known as the S wave). When these waves are taken together, they are known as the QRS complex.
The EKG, in practice, uses many sets of electrodes. But these electrodes are so arranged on the surface of the body such that the signal received will have the same shape as that just described. Well-known bipolar pairs of electrodes are typically located on a patient's right arm (RA), left arm (LA), right leg (RL) (commonly used as a reference), and left leg (LL). Monopolar electrodes referenced properly are referred to as V leads and are positioned anatomically on a patients chest according to an established convention. In heart monitoring and diagnosis, the voltage differential appearing between two such electrodes or between one electrode and the average of a group of other electrodes represents a particular perspective of the heart's electrical activity and is generally referred to as the EKG. Particular combinations of electrodes are called leads. For example, the leads which may be employed in a standard twelve-lead electrocardiogram system are:
Lead I=(LA-RA) PA1 Lead II=(LL-RA) PA1 Lead III=(LL-LA) PA1 Lead V1=V1-(LA+RA+LL)/3 PA1 Lead V2=V2-(LA+RA+LL)/3 PA1 Lead V3=V3-(LA+RA+LL)/3 PA1 Lead V4=V4-(LA+RA+LL)/3 PA1 Lead V5=V5-(LA+RA+LL)/3 PA1 Lead V6=V6-(LA+RA+LL)/3 PA1 Lead AVF=LL-(LA+RA)/2 PA1 Lead AVR=RA-(LA+LL)/2 PA1 Lead AVL=LA-(RA+LL)/2
Thus, although the term "lead" would appear to indicate a physical wire, in electrocardiography the term actually means the electrical signal taken from a certain electrode arrangement as illustrated above.
As alluded to above, the action potential which results in the contraction and beating of the heart has to be initiated by some agent. In the normal heart, this initiation is supplied by the sinoatrial node acting through the atrioventricular node. That is, the sinoatrial-atrioventricular complex acts to pace the firing of the heart muscle. However, in some instances, these natural pacemakers do not work correctly, and in those instances, control of cardiac activity by electric signal has proven to be useful.
The electric signal necessary is supplied by a pacing signal generator, which connects to the heart by a pair of pacing electrodes--a positive conductor and a negative conductor. The pacing generator takes the place of the body's malfunctioning natural pacemaker, and maintains a constant pulse rate by application of an electric pacing signal to the heart. The pacing signal provides an electric pulse, which gives rise to an organized contraction of the heart muscle fibers throughout the heart, thus causing the heart to beat. In other words, a pacing signal is a regulating signal for maintaining constant and effective pumping action by the heart.
For various reasons, medical professionals need to be able to view EKG data, even for a person with an electrical pacemaker. Unfortunately, for the same reasons that the EKG works, when the mechanical pacemaker discharges, it shows up as a deflection on an EKG. Furthermore, since the electrical pacemaker often discharges as a pulse of short time-duration, one can see that if the QRS complex is also of very short duration, which is very often the case for young pediatric patients and persons with various heart defects, it could be very difficult to select the pace pulse data from the QRS complex of the EKG. Thus, a need exists for a device which can easily and efficiently do this.
This need has not been satisfied, nor even generally recognized, in the prior art, as will be shown by the following summary of prior art references.
Wang et al (U.S. Pat. No. 4,838,278) disclose an apparatus for classifying the QRS complexes within EKG waveforms as dual-chamber paced, atrially paced, ventricularly paced, or unpaced, which is accomplished by comparing each acquired QRS complex with multiple pathologic QRS complexes stored in memory and making the assessment based upon pattern-matching between the acquired and stored complexes. Although Wang et al. recognize the difficulty in determining when a QRS complex and pacing pulse occur, Wang et al's disclosed apparatus utilizes a conventional pace pulse detector and conventional QRS detector to classify a QRS complex based upon the interval between the pacing pulse and the QRS complex. This reference does not consider nor discuss discriminating pace pulse data from EKG data that closely resemble pace-pulse data when measured by a single lead.
Wang et al. (U.S. Pat. No. 5,033,473) disclose a method and apparatus for discriminating between pace pulses and QRS complexes by determining whether a potential pace pulse tail exhibits an exponential decay in amplitude. Furthermore, this reference relates to detection of a largely obsolete form of pace pulse (with exponential tail). The present invention is not limited to this largely obsolete form of pace pulse. This reference does not consider nor discuss pulling pace pulse data from EKG data when they overlap very closely in time.
Kruse et al. (U.S. Pat. No. 5,448,997) disclose a pace pulse detector which utilizes multiple EKG leads to obtain a view of the heart from multiple angles. The pace pulse detector disclosed by Kruse et al. employs an algorithmic approach to pace-pulse discrimination which utilizes analog and digital filtering and signal processing to compare EKG waveform features with known amplitudes and spacings of pacing pulses. EKG waveform features matching the known amplitude and spacing characteristics of pacing pulses are then identified as pacing pulses. This reference does not consider nor discuss pulling pace-pulse data from EKG data when they overlap very closely in time; in fact, it appears that the method disclosed in this reference will not work if the pace pulse and the QRS complex are in identity, or very close thereto. Another distinction between the pace synchrony detector and the Kruse et al. patent is that the pace synchrony detector uses simultaneous information from multiple leads to develop information about conduction velocity, while the Kruse et al. patent uses multiple leads only to allow the selection of a single "best lead", after which this single lead is treated with conventional methods (pace width analysis primarily).
Sholder et al. (U.S. Pat. No. 4,817,605) discloses a pacemaker apparatus for achieving and maintaining atrial (P-wave) capture The output of the apparatus enables the monitoring of pacing pulses and P-waves, thereby enabling a physician to determine if atrial capture has been achieved by examining the time differential between the pacing pulses and the P-waves. Sholder et al. further discloses that the time differential between the pacing pulses and P-waves can be utilized to determine if a P-wave is generated in response to a pacing pulse or the activity of the sinus node of the heart utilizing known signal propagation characteristics of the heart. This reference does not consider nor discuss pulling pace-pulse data from EKG data when they overlap very closely in time. In fact, Sholder et al's patent refers to another class of apparatus, integrated with the pacemaker itself and having a prior knowledge of the timing of pace pulses. It is not really comparable with the problem of discriminating pace pulses from an ECG recording without this knowledge.
Shaya et al. (U.S. Pat. No. 4,664,116) disclose a pace-pulse identification apparatus which discriminates pacing pulses from other EKG wave features, including QRS complexes, on the basis of amplitude. Shaya et al's patent is fairly straight forward example of the class of detector the pace pulse synchrony detector improved upon by taking advantage of simultaneous lead information to calculate conduction velocities. This reference does not consider nor discuss pulling pace-pulse data from EKG data when they overlap very closely in time; in fact, it appears that the method disclosed in this reference will not work if the pace pulse and the QRS complex are in identity with respect to either time or amplitude.
As noted above, several of the references discovered by the search disclose systems which discriminate between pacing pulses and various waveform features, including QRS complexes. However, in contrast to the present invention, none of these disclose how to separate man-made pulses from the EKG data when the EKG has extremely narrow QRS complexes, such as are found in pediatric patents. Or, restated none of these disclose how to separate man-made pulses from the EKG data when the temporal or and frequency characteristics of the EKG data closely resemble man-made pulses.
In view of the foregoing, it should be apparent that a need exists for the present invention: an improved bioinstrumentation signal-processing system which can distinguish man-made electrical signals within the body from physiological electrochemical signals within the body when the man-made signals can overlap in time, and thus mimic, the physiological electrochemical activity within the body.